Multistage compressor for compressing gases

ABSTRACT

A multistage compressor ( 1 ) for compressing gases has a low-pressure range ( 7 ) and a high-pressure range ( 4 ), the high-pressure range ( 4 ) including at least one reciprocating compressor ( 3 ) driven via a crankshaft ( 5 ) and the low-pressure range ( 7 ) including at least one screw compressor ( 20 ) provided as a low-pressure compressor ( 6 ) having a rotating displacer ( 8 ) coupled to the crankshaft ( 5 ) of the reciprocating compressor ( 3 ).

The invention relates to a multistage compressor for compressing gases,having a low-pressure range and a high-pressure range, saidhigh-pressure range including at least one reciprocating compressordriven via a crankshaft and the low-pressure range including at leastone low-pressure compressor comprising a rotating displacer coupled tothe crankshaft of the reciprocating compressor. For the actuation of thecrankshaft, an electromotor, an internal combustion engine, a steamturbine or the like may, for instance, be provided.

With reciprocating compressors, compression in the low-pressure range,which may comprise several compression stages, is disadvantageous onaccount of the compressibility of the medium to be compressed, sincevery large reciprocating pistons and cylinder volumes are required,particularly at an intake in the atmospheric pressure range. Such largecylinders, on the one hand, give rise to technical problems because ofthe unfavorable stroke/bore ratio (the piston strokes of all compressorstages usually being identical and the cylinder diameters varying in theindividual pressure stages) and, on the other hand, involve extremelyhigh costs due to the dimensions of the valves, piston rings, etc.

For low-pressure range compression it has already been known to usecompressors (e.g., screw compressors, rotary compressors, etc.) whichare driven independently of a consecutively arranged reciprocatingcompressor and which operate more efficiently in the low-pressure rangethan reciprocating compressors. The thus precompressed medium is thenconducted on into a first compression stage in the consecutivelyarranged reciprocating compressor, where it is further compressed. Indoing so, it is, however, disadvantageous that the separate driving unitrequired for the low-pressure compressor calls for relatively large andexpensive multistage compressors.

Furthermore, a multistage reciprocating compressor prototypemanufactured by Bauer Kompressoren GmbH and exhibited at the Gastec Fairin Vienna in 1995 is known. That multistage compressor comprises aseparate reciprocating compressor directly coupled to the crankshaft ofa consecutively arranged multistage reciprocating compressor. Thereciprocating compressor directly coupled to the crankshaft of aconsecutively arranged multistage reciprocating compressor in that casemerely serves to suck empty the driving gear of the consecutivelyarranged multistage reciprocating compressor. The previously mentioneddisadvantages of a reciprocating compressor in the low-pressure rangeare thereby not overcome though.

In addition, an air compressor for aircraft engines is known from GB-597437 A, wherein a rotary compressor is provided in a low-pressure rangeand the air precompressed by the rotary compressor is subsequently fedto a multistage reciprocating compressor. The rotary compressor and thereciprocating compressor are both driven by a common crankshaft. Yet, itinvolves the disadvantage that a precompression of no more than 2.5 barcan be reached by the rotary compressor having dry lamellae.

GB-540 580 A likewise discloses an air compressor, in which a Rootsblower is provided to precompress air which is then conducted into areciprocating compressor for further compression. In that multistagecompressor, the crankshafts of the reciprocating compressors are coupledwith the drive shaft of the Roots blower not directly, but via belts.Again, precompression by the Roots blower is very low (2 bar at most).

It is the object of the invention to provide a multistage compressorand, in particular, a stationary compressor, which exhibits a compactmode of construction and, at the same time, is suitable for acomparatively high compression, wherein a higher pressure level thanhitherto known is to be reached already by low-pressure compression.Moreover, the multistage compressor is to be produced in a relativelycost-effective manner on account of its compact mode of construction.

The multistage compressor according to the invention of the initiallydefined kind is characterized in that at least one screw compressor isprovided as said low-pressure compressor. By coupling the screwcompressor to the crankshaft of the consecutively arranged reciprocatingcompressor, a multistage compressor is provided in which a separatedrive unit for the low-pressure compressor can be obviated, while acomparatively high precompression of up to a maximum of approximately 40bar is at the same time obtained in the low-pressure range.

In order to ensure a particularly compact and structurally simpleconfiguration of the compressor according to the invention, it will bebeneficial if the displacer of the screw compressor is directly coupledto the crankshaft of the reciprocating compressor. Such a direct screwcompressor/reciprocating compressor coupling not only allows for theomission of a separate drive unit for the screw compressor, but alsoenables the screw compressor to be directly driven by the crankshaft ofthe reciprocating compressor without providing an intermediate gear—atthe appropriate speed of the crankshaft.

For special applications of the multistage compressor, it isadvantageous with a view to providing a flexible arrangement of thescrew compressor relative to the crankshaft of the reciprocatingcompressor, if the displacer of the screw compressor is coupled to thecrankshaft of the reciprocating compressor by the aid of a couplingdevice transmitting the torque of the crankshaft. In this case it willbe favorable in most cases if a coupling device transmitting the speedof the crankshaft one-to-one is simply provided. A structurally simpleconfiguration of the coupling between the displacer of the low-pressurestage and the crankshaft of the high-pressure stage will be ensured, ifa chain drive or belt drive is provided as said coupling device.

In order to enable a multiplication or reduction of the speed of thecrankshaft relative to the speed of the displacer of the screwcompressor, it is advantageous if a toothed gearing is provided as saidcoupling device. Likewise, it may be beneficial in respect to themodular use of different previously arranged screw compressors, if aseparable coupling device is provided.

With a view to providing a particularly compact configuration of themultistage compressor, a reliable suction at atmospheric pressure and,in particular, favorable mounting conditions of the drive shaft and thecrankshaft, respectively, it is advantageous if the screw compressor isarranged on the reciprocating compressor side facing away from a driveunit of the multistage compressor.

Since screw compressors effect an internal compression of the aspiratedgas, thus raising the pressure and temperature of the gas, it isfavorable if a cooling device is provided in the gas duct between thereciprocating compressor and the screw compressor, since this will bothlimit any increase in temperature and reduce the necessary compressionwork.

When compressing moist gases, and hence particularly air, a certainquantity of the condensable gas portion will condense at an intermediatecooling. It is, therefore, advantageous if a condensate separator isprovided in the gas duct between the reciprocating compressor and thescrew compressor.

In order to restrict to the admissible value the final compressiontemperature in a compressor stage, it is advantageous if thelow-pressure compressor comprises several compression stages, since thiswill allow for operational savings as compared to single-stagecompression, enhance the volumetric efficiency and reduce the propulsionforces. If the reciprocating compressor comprises several compressionstages, the previously mentioned advantages will result as well.

In order to ensure an efficient compression of relatively large gasamounts, it is beneficial if several compression chambers are providedin parallel in a compression stage of the low-pressure compressor and/orthe reciprocating compressor.

In order to ensure an efficient automatic control of the wholemultistage compressor, it will be favorable if at least one controlmeans is arranged between the individual compressor stages, said controlmeans, for instance, being comprised of blow-off valves, by-pass valves,adjustable leak volumes, speed regulators and any other fittings. Inparticular, various mechanical, pneumatic, hydraulic, electric orelectronic components may be employed for the control or regulation ofthe multi-stage compressor, thus enabling both on-site control orregulation and remote control or regulation.

In the following, the invention will be explained in more detail by wayof preferred exemplary embodiments illustrated in the drawing, to whichit is, however, not to be restricted. In detail,

FIG. 1 represents a schematic view of a multistage compressor comprisinga reciprocating compressor in the high-pressure range and a screwcompressor;

FIG. 2 represents a schematic view of the multistage compressoraccording to FIG. 1, yet with a coupling device being arranged betweenthe low-pressure and high-pressure compressors;

FIG. 3 is a schematic cross section through a screw compressor;

FIG. 4 is a section along line VI-VI of FIG. 1.

FIG. 1 is a schematic view of a multistage compressor 1, in which thereciprocating compressor 3 of a high-pressure range 4 is driven by amotor 2. As a low-pressure compressor 6, a screw compressor 20 (cf. FIG.3) is coupled to the drive of the reciprocating compressor 3 in thelow-pressure range 7, whereby a rotating displacer 8 of the screwcompressor 20 is directly coupled to the crankshaft 5 of thereciprocating compressor 3. The direct coupling of the crankshaft 5 ofthe reciprocating compressor 3 with the displacer 8 of the screwcompressor 20 results in an extremely compact mode of construction ofthe multistage compressor 1, and it is, moreover, readily feasible toprovide a separate drive unit for the precompression of the gassubsequently high-compressed in the reciprocating compressor 3, by theaid of a screw compressor 20 comprising a rotating displacer 8. Unlikereciprocating compressors, screw compressors comprise compact, small andhence cost-effective structures, particularly at low-pressure intake ofgas 9, yet a precompression of up to 40 bar is nevertheless feasible bymeans of the screw compressor 20.

The gas compressed in the screw compressor 20 is subsequently conductedinto a first compressor stage 11 of the reciprocating compressor 3 (cf.FIG. 4) via a gas duct 10, wherein any desired control means may bearranged between the final compressor stage in the low-pressure rangeand a first compressor stage in the high-pressure range of thereciprocating compressor as well as individual compressor stages, e.g.,11, 12, 13 (cf. FIG. 4).

A cooling device 14 is shown, in particular, in FIG. 1 between thelow-pressure compressor 6 designed as a screw compressor 20 (cf. FIG. 3)and the reciprocating compressor 3, whereby a certain gas portion of thegas compressed in the low-pressure compressor 6 is caused to condense,which may be separated from the gas by the aid of a separator 15. Inaddition, a valve 16 is apparent, via which mass flows can be suppliedor discharged between the individual compressor stages.

FIG. 2 illustrates a multistage compressor 1 similar to that of FIG. 1,yet a toothed gearing 17 is interposed between the crankshaft 5 of thereciprocating compressor 3 and a drive shaft 5′ of the displacer 8 (cf.FIG. 3) of the screw compressor 20 to form a coupling device 18 betweenthe two shafts 5, 5′. Thus, a multiplication or reduction of the speedof the crankshaft 5 relative to the speed of the shaft 5′ driving thedisplacer 8 of the screw compressor 20 can be effected by the aid of thegearing 17.

FIG. 3 is a detailed schematic illustration of the screw compressor 20,by which a precompression up to about 40 bar can be effected by the aidof a displacer 8 directly coupled to the crankshaft 5 of thereciprocating compressor 3.

From the sectional illustration according to FIG. 4 it is apparent thatthe reciprocating compressor 3 comprises several compressor stages 11,12, 13, wherein the volume of the cylinder of the first compressor stage11, which is fed with the gas precompressed by the screw compressor 20provided as a low-pressure compressor 6, is the largest one and thevolumes of the consecutively arranged cylinders of compressor the stages12, 13 decrease with the compression increasing. Fittings of any type(not illustrated) may be provided between the individual compressorstages 11, 12, 13 for blow-off control and the like as well as for speedregulation. What is essential here is that the crankshaft 5 of thereciprocating compressor 3 is coupled with the rotor 8 of a low-pressurecompressor 6 either directly or via a coupling device.

1. A multistage compressor for compressing gases, comprising: a low-pressure range connected by a gas duct; and a high-pressure range, the high-pressure range including at least one reciprocating compressor driven via a crankshaft, the low-pressure range including at least one low-pressure compressor comprising a rotating displacer coupled to the crankshaft of the reciprocating compressor, wherein at least one screw compressor is provided as the low-pressure compressor, and a cooling device and a condensate separator are provided in the gas duct between the reciprocating compressor and the screw compressor, the screw compressor being arranged on a reciprocating compressor side facing away from a drive unit of the multistage compressor, and wherein the displacer of the screw compressor is directly coupled to the crankshaft of the reciprocating compressor such that the screw compressor is directly driven by the crankshaft of the reciprocating compressor.
 2. A multistage compressor according to claim 1, wherein a chain drive or a belt drive is provided as the coupling device.
 3. A multistage compressor according to claim 1, wherein a toothed gearing is provided as the coupling device.
 4. A multistage compressor according to claim 1, wherein the low-pressure compressor comprises several compressor stages.
 5. A multistage compressor according to claim 1, wherein the reciprocating compressor comprises several compressor stages.
 6. A multistage compressor according to claim 1, wherein several compressor chambers are provided in parallel in a compression stage of at least one of the low-pressure compressor and the reciprocating compressor.
 7. A multistage compressor according to claim 1, wherein at least one control means is arranged between the individual compressor stages.
 8. A multistage compressor for compressing gases, comprising: a low-pressure range connected by a gas duct; and a high-pressure range, the high-pressure range including at least one reciprocating compressor driven via a crankshaft, the low-pressure range including at least one low-pressure compressor comprising a rotating displacer coupled to the crankshaft of the reciprocating compressor, wherein at least one screw compressor is provided as the low-pressure compressor, and a cooling device and a condensate separator are provided in the gas duct between the reciprocating compressor and the screw compressor, the screw compressor being arranged on a reciprocating compressor side facing away from a drive unit of the multistage compressor, and wherein the displacer of the screw compressor is coupled to the crankshaft of the reciprocating compressor via a non-separable coupling device transmitting the torque of the crankshaft one-to-one such that the screw compressor is directly driven by the crankshaft of the reciprocating compressor.
 9. A multistage compressor according to claim 8, wherein a chain drive or a belt drive is provided as the coupling device.
 10. A multistage compressor according to claim 8, wherein a toothed gearing is provided as the coupling device.
 11. A multistage compressor according to claim 8, wherein the low-pressure compressor comprises several compressor stages.
 12. A multistage compressor according to claim 8, wherein the reciprocating compressor comprises several compressor stages.
 13. A multistage compressor according to claim 8, wherein several compressor chambers are provided in parallel in a compression stage of at least one of the low-pressure compressor and the reciprocating compressor.
 14. A multistage compressor according to claim 8, wherein at least one control means is arranged between the individual compressor stages. 